Orthopedic surgeon and stem-cell guru Brian Meh­ling, a fixture on the Manhattan social scene, runs the Blue Horizon Foundation — a group that throws swanky fund-raising galas and produces celebrity-hosted documentaries for orphans, yet doesn’t disclose its donations or how it spends them.

The IRS announced recently it revoked the foundation’s tax-exempt status last year for failure to provide tax returns for three consecutive years.

Several people listed as “advisory board members” on Blue Horizon’s Web site said they haven’t been involved with the charity for years. One adviser includes socialite Tabber Benedict, a lawyer serving prison time for a hit-and-run in the West Village.

Some members of the board admit they have no idea how the group’s huge private donations are being spent.

One former ally fumed: “I asked questions about how the money was being allocated. They just looked at me like I had three heads.”

A former advisory-board member said, “People ­donate big time to this cause, but we never see these numbers — they’re not made public.”

He admitted he does not donate but does attend the group’s parties: “Brian has these unbelievably opulent events for a charity of that size.”

But Mehling, 48, and his attorney told The Post that most of the foundation’s funding comes from his own pocket.

“People may get the perception that there’s huge amounts of money flowing in because they see a big gala, but there’s no money,” said lawyer James Moriarty. “There’s no money. If not for Brian’s medical practice, the group would not exist.”

The doctor claims he had no idea the IRS granted his group tax-exempt charity status because he had a falling-out with the law firm that filed the paperwork.

Blue Horizon’s last gala was at Guastavino’s in Midtown in October. Tickets for the event cost as much as $10,000 per table.

Last summer, Blue Horizon held events in the Hamptons to raise money for the gala. The group is still soliciting donations for the foundation online via PayPal.